title: Rapid reaction of nanomolar Mn(II) with superoxide radical in seawater and simulated freshwater.
abstract: Superoxide radical (O2-) has been proposed to be an important participant in oxidation-reduction reactions of metal ions in natural waters. Here, we studied the reaction of nanomolar Mn(II) with O2- in seawater and simulated freshwater, using chemiluminescence detection of O2- to quantify the effect of Mn(II) on the decay kinetics of O2-. With 3-24 nM added [Mn(II)] and <0.7 nM [O2-], we observed effective second-order rate constants for the reaction of Mn(II) with O2- of 6×10(6) to 1×10(7) M(-1)·s(-1) in various seawater samples. In simulated freshwater (pH 8.6), the effective rate constant of Mn(II) reaction with O2- was somewhat lower, 1.6×10(6) M(-1)·s(-1). With higher initial [O2-], in excess of added [Mn(II)], catalytic decay of O2- by Mn was observed, implying that a Mn(II/III) redox cycle occurred. Our results show that reactions with nanomolar Mn(II) could be an important sink of O2- in natural waters. In addition, reaction of Mn(II) with superoxide could maintain a significant fraction of dissolved Mn in the +III oxidation state.
authors.affiliation: Department of Chemistry and Geochemistry, Colorado School of Mines, Golden, Colorado 80401, United States. paul.hansard@dep.state.fl.us
authors.forename: S Paul
authors.initials: SP
authors.lastname: Hansard
authors.forename: Hillary D
authors.initials: HD
authors.lastname: Easter
authors.forename: Bettina M
authors.initials: BM
authors.lastname: Voelker
mesh_terms: D005618:Fresh Water / Q000737:chemistry*; D007700:Kinetics; D008345:Manganese / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D008956:Models, Chemical; D012623:Seawater / Q000737:chemistry*; D013481:Superoxides / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000737:chemistry
chemical_list: D014874:Water Pollutants, Chemical; D013481:Superoxides; D008345:Manganese